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/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    TreeNode* make(ListNode* start,ListNode* end){
        
        if(start==end) return NULL;
        ListNode* slow=start;
        ListNode* fast=start;
        while(fast!=end && fast->next!=end){
            slow=slow->next;
            fast=fast->next->next;
        }
        TreeNode* root= new TreeNode(slow->val);
        root->left=make(start,slow);
        root->right=make(slow->next,end);
        return root;
    }
    TreeNode* sortedListToBST(ListNode* head) {
        if(!head) return nullptr;
        TreeNode* res=make(head,NULL);
        return res;
    }
};